The present invention relates generally to terminations for connectors and more particularly to connectors used in connection with signal cables.
Many electronic devices rely upon transmission lines to transmit signals between related devices or between peripheral devices and circuit boards of a computer. These transmission lines incorporate signal cables that are capable of high-speed data transmissions.
These signal cables may use what are known as one or more twisted pairs of wires that are twisted together along the length of the cable, with each such twisted pair being encircled by an associated grounding shield. These twisted pairs typically receive complimentary signal voltages, i.e., one wire of the pair may see a +1.0 volt signal, while the other wire of the pair may see a xe2x88x921.0 volt signal. Thus, these wires may be called xe2x80x9cdifferentialxe2x80x9d pairs, a term that refers to the different signals they carry. As signal cables are routed on a path to an electronic device, they may pass by or near other electronic devices that emit their own electric field. These devices have the potential to create electromagnetic interference to transmission lines such as the aforementioned signal cables. However, this twisted pair construction minimizes or diminishes any induced electrical fields and thereby eliminates electromagnetic interference.
In order to maintain electrical performance integrity from such a transmission line, or cable, to the circuitry of an associated electronic device, it is desirable to obtain a substantially constant impedance throughout the transmission line, from circuit to circuit or to avoid large discontinuities in the impedance of the transmission line. The difficulty of controlling the impedance of a connector at a connector mating face is well known because the impedance of a conventional connector typically drops through the connector and across the interface of the two mating connector components. Although it is relatively easy to maintain a desired impedance through an electrical transmission line, such as a cable by maintaining a specific geometry or physical arrangement of the signal conductors and the grounding shield, an impedance drop is usually encountered in the area where a cable is mated to a connector. It is therefore desirable to maintain a desired impedance throughout the connector and its connection to the cable.
Typical signal cable terminations involve the untwisting of the wire pairs and the unbraiding of the braided shield wire surrounding the wire pairs. These wires are unbraided manually and this manual operation tends to introduce variability into the electrical performance. This is caused by unbraiding the grounding shield wires, then typically twisting them into a single lead and subsequently welding or soldering the twisted tail of a connector terminal. This unbraiding and twisting often results in moving the signal conductors and grounding shield out of their original state in which they exist in the cable. This rearrangement may lead to a decoupling of the ground and signal wires from their original state that may result in an increase of impedance through the cable-connector junction. Moreover, this twisting introduces mechanical variability into the termination area in that although a cable may contain multiple differential pairs, the length of the unbraided shield wire may vary from pair to pair. This variability and rearrangement changes the physical characteristics of the system in the termination area which may result in an unwanted change (typically an increase) in the impedance of the system in the area.
Additionally, it is common for the signal and ground termination tails of a connector to be arranged into whatever convenient space is present at the connector mounting face without any control of the geometry or spatial aspects of the signal and ground terminals being considered. When signal wires and ground shields are pulled apart from the end of a cable, an interruption of the cable geometry is introduced. It is therefore desirable to maintain this geometry in the termination area between the cable and the cable connector to reduce any substantial impedance increase from occurring due to the cable termination.
The present invention is therefore directed to a termination structure for providing improved connections between cables and connectors that provides a high level of performance and which maintains the electrical characteristics of the cable in the termination area.
Accordingly, it is a general object of the present invention to provide an improved termination structure for use in high-speed data transmission connections in which the impedance discontinuity through the cable termination is minimized so as to attempt to better match the impedance of the transmission line.
Another object of the present invention is to provide a termination assembly for use in conjunction with signal cables that provides a connection between the twisted wire pairs and grounding shield of the cable and the connector, the termination assembly having an improved electrical performance due to its structure, which eliminates large impedance discontinuities attributable to operator assembly.
A further object of the present invention is to provide an improved termination assembly for effecting a high-performance termination between a transmission line having at least one pair of differential signal wires and an associated ground and a connector having at least two signal and one ground terminal disposed adjacent to the signal terminals for contacting opposing corresponding signal ground terminals.
It is a further object of the present invention to provide such a connector wherein, by varying the size of the ground terminal and its location relative to its two associated signal wires, the impedance of the connector may be xe2x80x9ctunedxe2x80x9d to obtain a preselected impedance through the connector.
Yet another object of the present invention is to provide a connector for connecting cables, such as those of the IEEE 1394 type, to a circuit board of an electronic device, wherein the connector has a number of discrete, differential signal wires and associated grounds equal in number to those contained in the cables, the ground terminals of the connector being configured in size and location with respect to the signal terminals of the connector in order to minimize the drop in impedance through the connector.
It is a further object of the present invention to provide a termination assembly that provides a simple manner of termination for a signal cable in which the ground termination portion is both sized to control the impedance through the termination and to provide a nest for the grounding shield of the cable, the ground terminal portion of the connector being located rearwardly of the signal terminal portions to thereby permit the facilitation of the cable termination with selective stripping of the cable and minimal wire end preparation.
Yet still another object of the present invention is to provide a termination structure for a cable connector, the connector having a plurality of terminals, at least two of the terminals being signal terminals and one of the terminals being a ground terminal, each of the terminals having opposing contact and termination portions, the termination portions having the form of hollow, curved cups the signal terminal termination portion cups being circumscribed by the ground terminal termination portion cup so that the ground terminal termination portion cup serves to orient the shield of the cable in a preferred orientation and to direct the placement of the signal conductors of the cable in the signal termination cups.
Yet it is still another object of the present invention to provide a connector with a unique termination structure that is particularly suitable for termination to cables, the termination structure maintaining the mechanical arrangement of the cable conductors and grounding shield as they enter the cable connector so that the signal and ground wires are maintained in an orientation that emulates that of the cable.
Yet another object of the present invention is to provide a connector for termination to a cable, wherein the ground terminal is positioned within the cable connector housing and spaced apart from two associated signal terminals in the connector housing, the ground terminal having a body portion that is larger than corresponding body portions of the two signal terminal.
A yet further object of the present invention is to provide a cable connector for use with differential signal wire pairs extending the length of the cable, the cable connector having a ground terminal and two signal terminals that are arranged in a triangular orientation throughout the connector and the termination area thereof.
In order to obtain the aforementioned objects, one principal aspect of the invention that is exemplified by one embodiment thereof includes a first connector for a circuit board which has a housing having three conductive terminals in a unique pattern of a triplet, with two of the terminals carrying differential signals, and the remaining terminal being a ground terminal. A second connector for a cable is provided that mates with the first connector and this second connector also has a triplet pattern of conductive terminals that are terminated to signal and ground wires of the cable.
The arrangement of these three terminals within the connector permits the impedance to be more effectively controlled throughout the first connector, from the points of engagement with the cable connector terminals to be points of attachment to the circuit board. In this manner, each such triplet includes a pair of signal terminals that are aligned together in side-by-side order, and which are also spaced apart a predetermined distance from each other. A contact portion of the ground terminal extends along a different plane than that of like portions of the signal terminals, while the remainder of the ground terminal extends between the signal terminals, but along the same plane as the signal terminals.
The width of this ground terminal contact portion and its spacing from the signal terminals may be chosen so that the three terminals may have desired electrical characteristics such as capacitance and the like, which affect the impedance of the connector. The width of the ground terminal is usually increased in the contact mating area of the terminals and may also be increased in the transition area that occurs between the contact and termination areas of the terminals. By this structure, a greater opportunity is provided to reduce the impedance discontinuity which occurs in a connector without altering the mating positions or the pitch of the differential signal terminals. Hence, this aspect of the present invention may be aptly characterized as providing a xe2x80x9ctunablexe2x80x9d terminal arrangement for each differential signal wire pair and associated ground wire arrangement found either in a cable or in other circuits.
In another principal aspect of the present invention, two or more such tunable triplets may be provided within the connector housing, but separated by an extent of dielectric material, such as the connector housing, an air gap, or both. In order to maximize the high speed performance of such a connector, the signal and ground terminals preferably all have similar, flat contacts that are cantilevered from their associated body portions so that the ground terminal contact portions may be selectively sized with respect to their associated signal terminals to facilitate the tuning of the terminals to obtain the optimum desired impedance in the connector system. When two such triple terminal sets are utilized in the connectors of the present invention, power terminals of the connector may be situated between the two triple terminal sets at a level equal to that of the ground terminals so as not to interfere with the signal terminals.
In yet another principal aspect of the present invention, the width of the ground terminal through the cable connector is varied so as to present a different surface area that increases capacitive coupling between the ground and two differential signal terminals. This change in width occurs in the terminal body portion that is interposed between the contact and termination portions of the terminals. The widths and surface areas of the signal and ground terminals may be equal in the contact areas because the cable connector terminals, when in contact with the board connector, may take advantage of the differing widths and surface areas of the board connector ground terminal contact areas. The cable connector ground terminal body portion is then varied with respect to its associated signal terminal body portions to maintain a similar dimensional relationship and spacing, preferably maintaining the triangular orientation of the three terminals.
In still another principal aspect of the present invention, the cable connector ground terminal termination portions are arranged as demonstrated in another embodiment of the invention, in a triangular orientation to maintain the spatial relationships that occur among these three terminals in the terminal body portions that are housed in the cable connector. In the preferred execution of this embodiment, the termination portions of all the terminals are curved to define hollow xe2x80x9cnestsxe2x80x9d in receiving the cable wires therein.
Inasmuch as the size of the shield of the cable exceeds the size of internal wires, the ground termination nest is larger than the signal termination nests. The nests are preferably positioned so as to maintain the geometric relationship that exists between the signal wires and shield in the cable. The nests are preferably semi-circular to ensure accurate positioning of the signal conductors and the shield in the termination process. Thus, the ground terminal termination nest is positioned to receive and contact the grounding shield of the cable, while orienting the two signal conductors as they appear in the cable to facilitate the termination of them to the signal terminals of the cable connector.
The grounding shield termination nest extends along a semi-circular extent. If an imaginary line is drawn to continue this extent, it will encompass and enclose the signal termination nests. The termination portion nests may include extensions that extend outwardly and upwardly from the terminals, although the main extent of these terminals occurs in a general horizontal extent lengthwise out of the connector housing. These extents, as well as the center lines of the termination portions are arranged in the aforementioned triangular relationship with the ground terminal being spaced apart from and positioned above the two signal terminals. These and other objects, features and advantages of the present invention will be clearly understood through consideration of the following detailed description.